1. Field of the Invention
This invention relates to the field of data processing systems. More particularly, this invention relates to data processing systems in which multiple operating systems may be used and where an interrupt can occur and be serviced whilst an existing pending interrupt is already being serviced.
2. Description of the Prior Art
A data processing apparatus will typically include a processor for running applications loaded onto the data processing apparatus. The processor will operate under the control of an operating system. The data required to run any particular application will typically be stored within a memory of the data processing apparatus. It will be appreciated that the data may consist of the instructions contained within the application and/or the actual data values used during the execution of those instructions on the processor.
There arise many instances where the data used by at least one of the applications is sensitive data that should not be accessible by other applications that can be run on the processor. An example would be where the data processing apparatus is a smart card, and one of the applications is a security application which uses sensitive data, such as for example secure keys, to perform validation, authentication, decryption and the like. It is clearly important in such situations to ensure that such sensitive data is kept secure so that it cannot be accessed by other applications that may be loaded onto the data processing apparatus, for example hacking applications that have been loaded onto the data processing apparatus with the purpose of seeking to access that secure data.
In known systems, it has typically been the job of the operating system developer to ensure that the operating system provides sufficient security to ensure that the secure data of one application cannot be accessed by other applications running under the control of the operating system. However, as systems become more complex, the general trend is for operating systems to become larger and more complex, and in such situations it becomes increasingly difficult to ensure sufficient security within the operating system itself.
Examples of systems seeking to provide secure storage of sensitive data and to provide protection against malicious program code are those described in U.S. Patent Application US 2002/0007456 A1 and U.S. Pat. Nos. 6,282,657 B and 6,292,874 B.
Accordingly, it will be desirable to provide an improved technique for seeking to retain the security of such secure data contained within the memory of the data processing apparatus.